Steam turbine lubrication



X Patented Nov. 4, 1941 STEAM TURBINE LUBRICATION Albert G. Rocchini, Aspinwall, Pa., assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing.

Application April 5, 1940,

Serial 310,328,147 5 Claims. ((1252-56) This invention relates to steam turbine lubri-' cation; and it is particularly concerned with a method of preventing the corrosion of metal parts of steam turbines lubricated by a highly refined petroleum oil containing a phenolic antioxidant, wherein a minute amount of a higher fatty acid is incorporated in said oil; and it includes as an improved steam turbine lubricating oil a highly refined paraflinic lubricating oil containing a' small amount of a phenolicoxidation inhibitor and also a minute amount, advantageously 0.02 to 0.05 per cent, of a' higher fatty acid; all as more fully hereinafter set forth and as claimed.

In the lubrication of steam turbines, moderate- 1y refined and lightly refined petroleum oils have the disadvantage of being relatively unstable in service, developing organic acidity quite rapidly,

as evidencedeby a rise in neutralization number,

develppment of sludge. Furthermore; by incorporating in such highly refined oilscertain types of antioxidants which are resistant tosolution' in water and to hydrolysis, increase in neutralization number due to oxidation can be minimized.

I Certain of the phenolic oxidation inhibitors are particularly suitable in'this respect. It is desir-' --able therefore to lubricate steam turbines with highly refined paraifinic oils containing small amounts of phenolic antioxidants..-

However, it has been foundthat when such highly refined lubricating oils containing phenolic antioxidants are used to lubricate steam turbines, a certain amount of corrosion takes place, which isnot ordinarily encountered when the more moderately refined oils are used. This corrosion of the metal parts, particularly the steel parts, of the'turbine takes place during the early stages of the use of the oil. After the oil has been in use for a sufilcient-length of time the corrosive action stops, apparently because of a building up in the oil of some product which acts as a corrosion inhibitor.

The corrosion which takes place during the early stages of the use of a highly refined lubricating. oil in a steam turbine is 'not particularly extensive. It 'is, however, quite undesirable, because it often takes place in the governor. mechanism and very slight corrosion in this mecha: nism cuts down the clearances and throws the governor out of adjustment. It is desirable.

therefore, that even slight corrosion be prevented.

I have found that by incorporating a, minute amount of a higher fatty acid such as stearic acid, palmitic acid, oleic acid or mixtures-of these acids in a steam turbine oil consisting essentially of a highly refined parafiinic oil containing a small amount of a phenolic antioxidant, corrosion of metal parts of steam turbines in which such oil is used as a lubricant can be prevented and a steam turbine lubricating oil is obtained which is resistant to increase in neutralization number and steam emulsion number minum chloride refining, to remove all or substantially all of the unsaturated andnaphth enic constituents. An aluminum chloride refined paraifinic base oil, such as a Pennsylvania oil, provides the best type of highly refined oil for the purposes of my invention, although drastically refined Mid-Continent and Gulf Coastal oils I may also be used.

The oxidation inhibitors'which may be added to these highly refined lubricating oils for use in steam turbines are characterized by insolu-u bility in water and resistance to hydrolysis under the conditions of use. They should also be such that upon hydrolysis they do not, form compounds which are themselves acidic or corrosive. The water insoluble phenolic antioxidants such as beta-naphthol, p-benzyl-amino-phenol and the alkylated phenols, for example 2,6-di-tertiarybutyl-4-methyl phenol,

Of 'these, the water-insoluble alkylated phenols have proved most advantageous and are customarily used; use being in amounts corresponding to about 0.2 to 0.5 per cent by weight of the oil. When the other phenolic-inhibitors are used,

somewhat larger amounts are required, generally about 1.0 per cent.

According to the method of my invention, when a lubricating oil consisting essentially of a highly refined parafllnic oil and a small amount ofa water-insoluble phenolic oxidation inhibitor is to be used in a steam turbine, I preliminarily incorporate in the turbine oil a minute amount of a higher fatty acid. The higher fatty acid' serves to prevent corrosion particularlyof the steel parts of the turbine during the early stages of 2,4,6 -tri-tertiary-butyl phenol and the like, have been found suitable.

use of the oil and until the corrosion inhibiting products which form in the oil during use build up in quantity enough to prevent corrosion. The period required for building up this corrosion inhibiting property in the oil is relatively short and the amount of higher fatty acid required to be added to the oil to prevent corrosion during this period is very small. I have found that amounts of the saturatedhigher fatty acids, stearic acid or palmitic acid or mixtures of these acids, corresponding to about 0.02 to 0.05 per cent by weight of the oil are sumcient for this purpose. The unsaturated higher fatty acids such as oleic acid are also effective in these amounts but in general,

due to their unsaturated character may not be as desirable as the saturated higher fatty acids for long-time use.

The advantages of the incorporation of minute amounts of the higher fatty acids in highly refined steam turbine oils containing small amounts of phenolic oxidation inhibitors for prevention of corrosion of metal parts is illustrated in the following accelerated tests for stability against corrosion.

In these tests a highly refined paraifinic oil such as is used commercially for the lubrication of steam turbines, being an aluminum chloride refined Pennsylvania paramn base oil having a viscosity at 100 of 150 and an A. PQI. gravity of.

32.5", was used. The effect of a sample of this oil containing 0.2 per cent of 2,6-di-tertiarybutyl-4-methyl phenol on polished cold rolled steel strips in the presence of water was compared with the. effect of another sample containing 0.2

per cent of 2,6-di-tertiary-butyl-4-rnethyl phenol and 0.02 per cent of stearic acid.

for corrosion. I The steel strip which had been immersed in the.

highly refined oil containing the alkylated'phenol antioxidant but no saturated higher fatty acid fined lubricating oil containing both the alkylated phenol antioxidant and the stearic acid was clean and bright and showed no' rust, indicating the protective effect of the higher fatty acid.

Similar tests carried out at temperatures of 140 F. and in which fresh water was added to the oil daily also showed no rusting of the steel samples immersed in oils containing 0.02 per cent oleic acid and 0.02 per cent stearic acid respectively.

The invention has been described with particular reference to certain specific embodiments thereof by way of illustration and example, but it is to be understood that this invention is not limited to such embodiments except as hereinafter defined in the appended claims. 9

What I claim is: l

1. A method of preventing the corrosion of metal parts of steam turbines lubricated by a highly refined parafilnic oil containing a phenolic antioxidant, comprising incorporating in said lubricating oil prior to use a minute amount of a showed rust formation on its surfaces while the 5 strip which had been immersed in the highly reing in said lubricating oil a minute amount of higher fatty acid selected from the group con- I sisting of stearic acid, palmitic acid, oleic 'acid and mixtures thereof.

3. A method of preventing the corrosion of' metal parts of steam turbines lubricated by a' highly refined par'afiinic oil containing a phenolic antioxidant, comprising preliminarily incorporating insaid lubricatingoil 0.02 to 0.05 per cent of a higher fatty acid selected-from the group consisting of 'stearic acid, palmitic acid, oleic acid and mixtures thereof.

4. An improved steam turbine qil consisting essentially of a highly refined parafiinic oil containing a phenolic antioxidant and -also 0.02 to, 0.05 per cent of a higher fatty acid.

5. An improved steam turbine oil consisting essentially of a highly refined parafiinic oil containing a .phenolic antioxidant and also 0.02 to 0.05 per cent of a higher fatty acid selected from the group consisting of stearic acid, palmitic acid, oleic acid and mixtures thereof.

ALBERT G. aoccmm. 

